1. Field of the Invention
The present invention relates to an exposure apparatus that exposes a pattern on a substrate via a projection optical system and a liquid and to device manufacturing method.
2. Description of Related Art
The semiconductor device or the liquid crystal display device is manufactured by the technique known as photolithography, in which a pattern formed on a mask is transferred onto a photosensitive substrate. The exposure apparatus used in this photolithography process has a mask stage that supports a mask and a substrate stage that supports a substrate, and it transfers a mask pattern to a substrate via a projection optical system while sequentially moving the mask stage and the substrate stage. In recent years, it is demanded to realize the higher resolution of the projection optical system in order to respond to the further advance of the higher integration of the device pattern. As the exposure wavelength to be used is shorter, the resolution of the projection optical system becomes higher. As the numerical aperture of the projection optical system is larger, the resolution of the projection optical system becomes higher. Therefore, the exposure wavelength, which is used for the exposure apparatus, is shortened year by year, and the numerical aperture of the projection optical system is increased as well. The exposure wavelength, which is dominantly used at present, is 248 nm of the KrF excimer laser. However, the exposure wavelength of 193 nm of the ArF excimer laser, which is shorter than the above, is also practically used in some situations. When the exposure is performed, the depth of focus (DOF) is also important in the same manner as the resolution. The resolution R and the depth of focus δ are represented by the following expressions respectively.R=k1·λ/NA,   (1)δ=±k2·λ/NA2,   (2)
In the expressions, λ represents the exposure wavelength, NA represents the numerical aperture of the projection optical system, and k1 and k2 represent the process coefficients. According to the expressions (1) and (2), the following fact is appreciated. That is, when the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ is narrowed.
If the depth of focus δ is too narrowed, it is difficult to match the substrate surface with respect to the image plane of the projection optical system. It is feared that the margin is insufficient during the exposure operation. Accordingly, the liquid immersion method has been suggested, which is disclosed, for example, in PCT International Publication No. WO99/49504 as a method for substantially shortening the exposure wavelength and widening the depth of focus. In this liquid immersion method, the space between the lower surface of the projection optical system and the substrate surface is filled with a liquid such as water or any organic solvent to form a liquid immersion area so that the resolution is improved and the depth of focus is magnified about n times by utilizing the fact that the wavelength of the exposure light beam in the liquid is 1/n as compared with that in the air (n represents the refractive index of the liquid, which is about 1.2 to 1.6 in ordinary cases). As far as is permitted by the law of the country specified or selected in this patent application, the disclosures in PCT International Publication No. WO99/49504 are incorporated herein by reference.
If the supply of liquid from the supply port of the liquid supply mechanism is uneven when the liquid is supplied onto the substrate to form a liquid immersion region, there is a possibility of occurrence of an inconvenience such as the formation of the liquid immersion region becoming inadequate, leading to deterioration of the pattern image exposed onto the substrate. For this reason, even (uniform) supply of liquid from the supply port of the liquid supply mechanism is also in demand. The prevention of mixing in of impurities such as bubbles, etc. into the liquid immersion region is also in demand in order to prevent deterioration of the pattern image exposed on the substrate.
Furthermore, it is also important that the liquid on the substrate be recovered well. When the liquid cannot be adequately recovered, for example, the liquid that remains on the substrate dries, a water mark is produced there, and an inconvenience in which the remaining liquid is scattered to the peripheral mechanical components when, for example, the substrate is conveyed and rust is caused also occurs. In addition, when liquid remains and is scattered, there is a possibility that the measuring operations relating to exposure processing will be affected, such as by fluctuations being brought about in the environment (temperature, etc.) in which the substrate is placed, causing changes in the refractive index on the optical path of the detection light of the optical interferometer used in stage position measurement, thereby causing exposure precision to degraded.